During the process of directional drilling, real time bore hole positioning data as well as formation evaluation data is needed in order to effectively steer the well bore to the correct trajectory. These tools are interchangeably referred to as Measurement While Drilling (MWD) or Logging While Drilling (LWD) tools.
A typical MWD tool (also named string) is located in a nonmagnetic drill collar as part of the bottom hole assembly (BHA) throughout the drilling process. The MWD tool can be mechanically fixed to the collar (bolted in a special sub) or can be resting on a mechanical support and kept down gravitationally and with the aid of flow. To obtain accurate readings the tool must be as close to the drill bit as possible, maintain a particular rotational alignment with the high side of a motor's curvature and be separated by a minimum distance from any magnetic material in the drill string. Additionally, the tool must be mounted in such a way as to permit transmission of the signal by EM, Mud Pulse, or alternate telemetry system. Typically this mounting is completed as part of the telemetry system on a terminal end of the string.
As a result of the proximity of the MWD tool to the mud motor and the bit, it is exposed to an environment that has the highest vibration and shock loads in the drill string. Where MWD tools were historically able to withstand these loads, improved technology such as, increasingly aggressive drill bits, stronger mud motors, and devices such as agitators (specifically designed to incite a vibration in the drill string) are being used to increase the rates of penetration (ROP) and extend the depth and reach of directional wells resulting in a much more aggressive environment. As a result, the typical drilling environment is now so violent that MWD tools are no longer able to survive for extended or even moderate periods of time resulting in failures of the tools that can cause significant time and monetary losses to the drilling operator as well as the MWD supplier that must replace or repair the damaged equipment. The most pressing and damaging of these vibrational loads continues to be those applied along the long axis of the drill string (referred as axial vibration or vibration along the Z axis).
While various technologies have been developed in the past to mitigate these issues, each one of them is associated with specific shortcomings that have necessitated further development. For instance, solutions have been developed that are integrated directly into the drill string, these are referred to as “Shock Subs”, “Shocks” or “Thrusters”. Regardless of the specific design or technology used, all drill string based solutions necessarily increase the distance from the MWD sensor to the drill bit and can reduce the effectiveness of the agitator and can negatively affect drilling dynamics and cause a reduction in ROP.
Other systems have been developed integral to MWD strings such as rubber encased connections between electronics design to absorb shock; however these are ineffective at damping large displacements and low excitation frequencies, and only protect certain elements of the string.
In another attempt to solve this issue newly designed systems have tried to protect the MWD string as a whole, however, currently they are limited in that their design necessitates a location in the tool where no electrical wiring is needed, limiting its compatibility with certain MWD string geometries. Alternate designs are also known to use “sliding spline” or “sliding pin” systems as a means for transmitting torque while allowing axial motion. These sliding pin systems comprise either a pin axially moveable in a slot, or a cooperative arrangement of axial splines or ribs between components. They are particularly prone to a high degree of wear due to the sliding contact which results in a number of problems such as allowing some torsional or twisting movement or backlash between housings, which can actually increase torsional vibration in the tool; creating wear product that contaminates the tool environment and can cause further damage to other components and excessive frictional heat generation, which can be damaging to other components nearby. These tools are also longer and less robust due to the use of coil or disc springs, and are designed for use with specific narrow MWD string configurations and weights, limiting their use in the general case.
Details of the tools described above can be found in the prior art:                US 20150376959 A1—Axial Lateral and Torsional Force Dampener        U.S. Pat. No. 8,640,795 B2—Shock Reduction Tool For a Downhole Electronics Package        US 2009/0023502—Downhole Shock Absorber for Torsional and Axial Loads        U.S. Pat. No. 3,406,537—Shock Absorbing Sub Assembly        U.S. Pat. No. 5,083,623—Hydraulic Shock Absorber        WO 2015168226 A1—Snubber for Downhole Tool        U.S. Pat. No. 4,186,569 A—Dual Spring Drill String Shock Absorber        US 20130206395 A1—Method and Apparatus for Reducing Shock and Vibration in Down Hole Tools        
In view of the above limitations, there is need for a tool that can isolate the MWD String from the axial vibration while allowing a plurality of electrical paths through the tool, maintaining rotational alignment without excessive sliding friction, allowing for placement in any location of any tool string.